A power device using Si is employed in the field of power electronics such as motor control of a motor vehicle and an electric train, and the like. The insulation resistance of the power device depends on the performance limit of the power device. Therefore, there has been required the material having a wider band gap and higher breakdown field strength than Si. Silicon carbide (SiC), GaN, or diamond all has a wider band gap and higher breakdown field strength than Si. In addition, such material has the advantages such as a high saturated drift velocity, high stability at a high temperature, and the like.
In comparison of physical properties of SiC with those of Si, SiC is about two to three times wider in band gap, about one digit higher in breakdown field strength, and several times higher in saturated drift velocity than Si. Moreover, in comparison with another wide band gap semiconductor, SiC has superior matching with silicon based process, because SiO2 can be made from SiC by thermal oxidation. Alternatively, because use of SiC allows a user to control p and n type conduction by impurity doping, SiC has advantages in terms of practical use.
A SiC single-crystal epitaxial film is grown with chemical vapor deposition (CVD) method, a sublimation method, or the like. Film growth with CVD method is carried out using SiH4, C3H8, and H2 at a temperature more than 1,500 degrees C. in a hot-wall CVD reactor. Also, SiC powder confined in a crucible is heated up to nearly 2,000 degrees C. to grow SiC on a substrate in the sublimation method. A sublimation method has advantageously a fast growth rate in comparison with CVD method.
Although a SiC epitaxial film can be formed by various methods, defects have not been reduced sufficiently for the required element performance. The crystal defect represented by dislocation is a factor in degradation of element characteristics such as a withstanding pressure and the like. Therefore, various contrivances have been made. Japanese Patent Laid-Open publication No. 2005-350278 is the one example. Patent document 1: Japanese Patent Laid-Open publication No. 2005-350278
In the procedure of forming a SiC element, the thermal treatment at high temperatures of around 1,200 to 1,800 degrees C. is necessary for activation of dopants and the like. Recrystallization can spread a defect into a high quality region with few defects and furthermore can reduce the element yield.
Also, a large-diameter semiconductor wafer (with a diameter of, for example, 6 inches) is currently required, and therefore a bowing of a SiC substrate having a SiC film formed by epitaxial growth becomes a serious problem. It is necessary to use a stepper (reduction projection exposure apparatus) for the patterning equal to or less than 1 μm (micrometer). The SiC substrate with a large bowing equal to or more than several tens of μm (micrometer) makes a fine pattern formation difficult.